Information about Molecule
In chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two atoms in a definite arrangement held together by strong chemical bonds.[1][2] In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules and biomolecules.
Molecules are distinguished from polyatomic ions in the strict sense.
This definition has evolved as knowledge of the structure of molecules has increased. Earlier definitions were less precise defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties.[3] This definition often breaks down since many substances in ordinary experience, such as rocks, salts, and metals, are composed of atoms or ions, but are not made of molecules.
In the kinetic theory of gases the term molecule is often used for any gaseous particle regardless of their composition.[4] According to this definition noble gases would also be considered molecules despite the fact that they are composed of a single non-bonded atom.
The term "molecule", from the French molécule meaning "extremely minute particle," was coined by French philosopher Rene Descartes in the 1620s. Although the existence of molecules was accepted by many chemists since the early 19th century as a result of Dalton's laws of Definite and Multiple Proportions (1803-1808) and Avogadro's law (1811), there was some resistance among positivists and physicists such as Mach, Boltzmann, Maxwell, and Gibbs, who saw molecules merely as convenient mathematical constructs. The work of Perrin on Brownian motion (1911) is considered to be the final proof of the existence of molecules.
In a molecule, at least two atoms are joined by shared pairs of electrons in a covalent bond. It may consist of atoms of the same chemical element, as with oxygen (O2), or of different elements, as with water (H2O). Atoms and complexes connected by non-covalent bonds such as hydrogen bonds or ionic bonds are generally not considered single molecules.
No typical molecule can be defined for ionic (salts) and covalent crystals (network solids) which are composed of repeating unit cells that extend either in a plane (such as in graphite) or three-dimensionally (such as in diamond or sodium chloride).
The science of molecules is called molecular chemistry or molecular physics, depending on the focus. Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds, while molecular physics deals with the laws governing their structure and properties. In practice, however, this distinction is vague. In molecular sciences, a molecule consists of a stable system (bound state) comprising two or more atoms. Polyatomic ions may sometimes be usefully thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i.e., short-lived assemblies (resonances) of electrons and nuclei, such as radicals, molecular ions, Rydberg molecules, transition states, van der Waals complexes, or systems of colliding atoms as in Bose-Einstein condensates.
The molecular mass can be calculated from the chemical formula and is expressed in conventional atomic mass units equal to 1/12th of the mass of a neutral carbon-12 (12C isotope) atom. For network solids, the term formula unit is used in stoichiometric calculations.
Molecules have fixed equilibrium geometries—bond lengths and angles— about which they continuously oscillate through vibrational and rotational motions. A pure substance is composed of molecules with the same average geometrical structure. The chemical formula and the structure of a molecule are the two important factors that determine its properties, particularly its reactivity. Isomers share a chemical formula but normally have very different properties because of their different structures. Stereoisomers, a particular type of isomers, may have very similar physico-chemical properties and at the same time very different biochemical activities.
There are four statements of facts concerning molecules. These facts are:
1. All matter are composed of tiny particles called molecules.
2. There are spaces between molecules.
3. Molecules are constantly moving.
4. Molecules attract one another.
These statements together form the Molecular Theory.
Molecular spectroscopy deals with the response (spectrum) of molecules interacting with probing signals of known energy (or frequency, according to Planck's formula). Scattering theory provides the theoretical background for spectroscopy.
The probing signal used in spectroscopy can be an electromagnetic wave or a beam of particles (electrons, positrons, etc.) The molecular response can consist of signal absorption (absorption spectroscopy), the emission of another signal (emission spectroscopy), fragmentation, or chemical changes.
Spectroscopy is recognized as a powerful tool in investigating the microscopic properties of molecules, in particular their energy levels. In order to extract maximum microscopic information from experimental results, spectroscopy is often coupled with chemical computations.
When trying to define rigorously whether an arrangement of atoms is "sufficiently stable" to be considered a molecule, IUPAC suggests that it "must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state".[1] This definition does not depend on the nature of the interaction between the atoms, but only on the strength of the interaction. In fact, it includes weakly-bound species that would not traditionally be considered molecules, such as the helium dimer, He2, which has one vibrational bound state but is so loosely bound that it is only likely to be observed at very low temperatures.
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This definition has evolved as knowledge of the structure of molecules has increased. Earlier definitions were less precise defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties.[3] This definition often breaks down since many substances in ordinary experience, such as rocks, salts, and metals, are composed of atoms or ions, but are not made of molecules.
In the kinetic theory of gases the term molecule is often used for any gaseous particle regardless of their composition.[4] According to this definition noble gases would also be considered molecules despite the fact that they are composed of a single non-bonded atom.
History
The term "molecule", from the French molécule meaning "extremely minute particle," was coined by French philosopher Rene Descartes in the 1620s. Although the existence of molecules was accepted by many chemists since the early 19th century as a result of Dalton's laws of Definite and Multiple Proportions (1803-1808) and Avogadro's law (1811), there was some resistance among positivists and physicists such as Mach, Boltzmann, Maxwell, and Gibbs, who saw molecules merely as convenient mathematical constructs. The work of Perrin on Brownian motion (1911) is considered to be the final proof of the existence of molecules.
In a molecule, at least two atoms are joined by shared pairs of electrons in a covalent bond. It may consist of atoms of the same chemical element, as with oxygen (O2), or of different elements, as with water (H2O). Atoms and complexes connected by non-covalent bonds such as hydrogen bonds or ionic bonds are generally not considered single molecules.
No typical molecule can be defined for ionic (salts) and covalent crystals (network solids) which are composed of repeating unit cells that extend either in a plane (such as in graphite) or three-dimensionally (such as in diamond or sodium chloride).
The science of molecules is called molecular chemistry or molecular physics, depending on the focus. Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds, while molecular physics deals with the laws governing their structure and properties. In practice, however, this distinction is vague. In molecular sciences, a molecule consists of a stable system (bound state) comprising two or more atoms. Polyatomic ions may sometimes be usefully thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i.e., short-lived assemblies (resonances) of electrons and nuclei, such as radicals, molecular ions, Rydberg molecules, transition states, van der Waals complexes, or systems of colliding atoms as in Bose-Einstein condensates.
Molecular size
Most molecules are far too small to be seen with the naked eye, but there are exceptions. DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers. The smallest molecule is the diatomic hydrogen (H2), with an overall length of roughly twice the 74 picometres (0.74 Å) bond length. Molecules commonly used as building blocks for organic synthesis have a dimension of a few Å to several dozen Å. Single molecules cannot usually be observed by light (as noted above), but small molecules and even the outlines of individual atoms may be traced in some circumstances by use of an atomic force microscope. Some of the largest molecules are macromolecules or supermolecules.Molecular formula
The empirical formula of a molecule is the simplest integer ratio of the chemical elements that constitute the compound. For example, in their pure forms, water is always composed of a 2:1 ratio of hydrogen to oxygen, and ethyl alcohol or ethanol is always composed of carbon, hydrogen, and oxygen in a 2:6:1 ratio. However, this does not determine the kind of molecule uniquely - dimethyl ether has the same ratio as ethanol, for instance. Molecules with the same atoms in different arrangements are called isomers. The empirical formula is often the same as the molecular formula but not always. For example the molecule acetylene has molecular formula C2H2, but the simplest integer ratio of elements is CH. The molecular formula reflects the exact number of atoms that compose a molecule.The molecular mass can be calculated from the chemical formula and is expressed in conventional atomic mass units equal to 1/12th of the mass of a neutral carbon-12 (12C isotope) atom. For network solids, the term formula unit is used in stoichiometric calculations.
Molecular geometry
Molecules have fixed equilibrium geometries—bond lengths and angles— about which they continuously oscillate through vibrational and rotational motions. A pure substance is composed of molecules with the same average geometrical structure. The chemical formula and the structure of a molecule are the two important factors that determine its properties, particularly its reactivity. Isomers share a chemical formula but normally have very different properties because of their different structures. Stereoisomers, a particular type of isomers, may have very similar physico-chemical properties and at the same time very different biochemical activities.
Molecular Theory
There are four statements of facts concerning molecules. These facts are:
1. All matter are composed of tiny particles called molecules.
2. There are spaces between molecules.
3. Molecules are constantly moving.
4. Molecules attract one another.
These statements together form the Molecular Theory.
Molecular spectroscopy
Molecular spectroscopy deals with the response (spectrum) of molecules interacting with probing signals of known energy (or frequency, according to Planck's formula). Scattering theory provides the theoretical background for spectroscopy.
The probing signal used in spectroscopy can be an electromagnetic wave or a beam of particles (electrons, positrons, etc.) The molecular response can consist of signal absorption (absorption spectroscopy), the emission of another signal (emission spectroscopy), fragmentation, or chemical changes.
Spectroscopy is recognized as a powerful tool in investigating the microscopic properties of molecules, in particular their energy levels. In order to extract maximum microscopic information from experimental results, spectroscopy is often coupled with chemical computations.
Theoretical aspects
The study of molecules by molecular physics and theoretical chemistry is largely based on quantum mechanics and is essential for the understanding of the chemical bond. The simplest of molecules is the hydrogen molecule-ion, H2+, and the simplest of all the chemical bonds is the one-electron bond. H2+ is composed of two positively-charged protons and one negatively-charged electron bound by photon exchange, which means that the Schrödinger equation for the system can be solved more easily due to the lack of electron–electron repulsion. With the development of fast digital computers, approximate solutions for more complicated molecules became possible and are one of the main aspects of computational chemistry.When trying to define rigorously whether an arrangement of atoms is "sufficiently stable" to be considered a molecule, IUPAC suggests that it "must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state".[1] This definition does not depend on the nature of the interaction between the atoms, but only on the strength of the interaction. In fact, it includes weakly-bound species that would not traditionally be considered molecules, such as the helium dimer, He2, which has one vibrational bound state but is so loosely bound that it is only likely to be observed at very low temperatures.
See also
- Molecular modelling
- Covalent bond
- Diatomic molecule
- History of the molecule
- Molecular geometry
- Molecular Hamiltonian
- Molecular orbital
- Nonpolar molecule
- Polar molecule
- For a list of molecules see the List of compounds
- List of molecules in interstellar space
References
1. ^ International Union of Pure and Applied Chemistry (1994). "molecule". Compendium of Chemical Terminology Internet edition.
2. ^ Pauling, Linus (1970). General Chemistry. New York: Dover Publications, Inc.. ISBN 0-486-65622-5.
Ebbin, Darrell, D. (1990). General Chemistry, 3th Ed.. Boston: Houghton Mifflin Co.. ISBN 0-395-43302-9.
Brown, T.L. (2003). Chemistry – the Central Science, 9th Ed.. New Jersey: Prentice Hall. ISBN 0-13-066997-0.
Chang, Raymond (1998). Chemistry, 6th Ed.. New York: McGraw Hill. ISBN 0-07-115221-0.
Zumdahl, Steven S. (1997). Chemistry, 4th ed.. Boston: Houghton Mifflin. ISBN 0-669-41794-7.
3. ^ Molecule Definition (Frostburg State University)
4. ^ E.g. see [1]
2. ^ Pauling, Linus (1970). General Chemistry. New York: Dover Publications, Inc.. ISBN 0-486-65622-5.
Ebbin, Darrell, D. (1990). General Chemistry, 3th Ed.. Boston: Houghton Mifflin Co.. ISBN 0-395-43302-9.
Brown, T.L. (2003). Chemistry – the Central Science, 9th Ed.. New Jersey: Prentice Hall. ISBN 0-13-066997-0.
Chang, Raymond (1998). Chemistry, 6th Ed.. New York: McGraw Hill. ISBN 0-07-115221-0.
Zumdahl, Steven S. (1997). Chemistry, 4th ed.. Boston: Houghton Mifflin. ISBN 0-669-41794-7.
3. ^ Molecule Definition (Frostburg State University)
4. ^ E.g. see [1]
External links
- Molecule of the Month - School of Chemistry, University of Bristol
- Antibody Molecule - The National Health Museum
- Data Book of Molecules - Home Page for Learning Environmental Chemistry
Particles in physics | |
|---|---|
| Elementary particles | Elementary fermions: Quarks: u d s c b t • Leptons: e μ τ νe νμ ντ Elementary bosons: Gauge bosons: γ g W Z0 • Ghosts |
| Composite particles | Hadrons: Baryons(list)/Hyperons/Nucleons: p n Δ Λ Σ Ξ Ω Ξb • Mesons(list)/Quarkonia: π K ρ J/ψ Υ Other: Atomic nucleus • Atoms • Molecules • Positronium |
| Hypothetical elementary particles | Superpartners: Axino Dilatino Chargino Gluino Gravitino Higgsino Neutralino Sfermion Slepton Squark Other: Axion Dilaton Goldstone boson Graviton Higgs boson Tachyon X Y W' Z' |
| Hypothetical composite particles | Exotic hadrons: Exotic baryons: Pentaquark • Exotic mesons: Glueball Tetraquark Other: Mesonic molecule |
| Quasiparticles | Davydov soliton Exciton Magnon Phonon Plasmon Polariton Polaron |
| Organism→System→Organ→Tissue→Cell→Organelle→Molecule→Atom→Subatomic particle→Elementary particle |
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Flavour in particle physics
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atom (Greek ἄτομος or átomos meaning "indivisible") is the smallest particle still characterizing a chemical element.
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A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds.
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Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting primarily of carbon and hydrogen, which may
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Biochemistry is the study of the chemical processes in living organisms.[1] The word "biochemistry" comes from the Greek word βιοχημεία biochēmeia, which means "the chemistry of life.
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organic compounds]] An organic compound is any member of a large class of chemical compounds whose molecules contain carbon; for historical reasons discussed below, a few types of compounds such as carbonates, carbon oxides and cyanides, as well as elemental carbon are
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biomolecule is a chemical molecule that naturally occurs in living organisms. Biomolecules consist primarily of carbon and hydrogen, along with nitrogen, oxygen, phosphorus and sulfur. Other elements sometimes are incorporated but are much less common.
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polyatomic ion is a molecule that bears ionic groups, that is, a molecule with a charge. The majority of biological compounds and inorganic species conform to this strict definition.
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Balanced Rock stands in Garden of the Gods park in Colorado Springs, CO]] A rock is a naturally occurring aggregate of minerals and/or mineraloids. The Earth's lithosphere is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic.
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Salt is a mineral essential for animal life, composed primarily of sodium chloride. Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt.
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The Macro Expansion Template Attribute Language complements TAL, providing macros which allow the reuse of code across template files. Both were created for Zope but are used in other Python projects as well.
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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Kinetic theory or kinetic theory of gases attempts to explain macroscopic properties of gases, such as pressure, temperature, or volume, by considering their molecular composition and motion.
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Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape. Compared to the solid and liquid states of matter a gas has lower density and a lower viscosity.
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noble gases are the elements in group 18 (also sometimes Group 0 IUPAC Style, or Group 8) of the periodic table. It is also called helium family or neon family.
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history of the molecule traces the origins of the concept or idea of the existence, in nature, of a bonded structure of two or more atoms, according to which the structures of the universe are built.
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René Descartes (French IPA: [ʁə'ne de'kaʁt]) (March 31, 1596 – February 11, 1650), also known as Renatus Cartesius
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John Dalton (September 6, 1766 – July 27, 1844) was an English chemist, meteorologist and physicist, born at Eaglesfield, near Cockermouth in Cumbria. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness
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Avogadro's law (Avogadro's Hypothesis, or Avogadro's Principle) is a gas law named after Amedeo Avogadro, who in 1811 hypothesized that:
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- Equal volumes of gases, at the same temperature and pressure, contain the same number of particles, or molecules.
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Logical positivism grew from the discussions of Moritz Schlick's Vienna Circle and Hans Reichenbach's Berlin Circle in the 1920s and 1930s. The movement is known for its espousal of verificationism, its admiration for science and technical rigor, and its commitment to the
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Ernst Mach (pronounced [max], see IPA) (February 18, 1838 – February 19, 1916) was a Bohemian-Austrian physicist and philosopher and is the namesake for the "Mach number" (also known as Mach speed) and the optical illusion known as Mach bands.
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Ludwig Boltzmann
Ludwig Eduard Boltzmann (1844-1906)
Born January 20 1844
Vienna, Austrian Empire
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Ludwig Eduard Boltzmann (1844-1906)
Born January 20 1844
Vienna, Austrian Empire
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James Clerk Maxwell
James Clerk Maxwell
Born May 13 1831
Edinburgh, Scotland
Died November 5 1879 (aged 48)
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James Clerk Maxwell
Born May 13 1831
Edinburgh, Scotland
Died November 5 1879 (aged 48)
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J. Willard Gibbs
(1839-1903)
Born January 11 1839
New Haven, Connecticut, U.S.
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(1839-1903)
Born January 11 1839
New Haven, Connecticut, U.S.
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Jean Baptiste Perrin
Jean Baptiste Perrin, ca. 1926
Born September 30 1870
Lille, France
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Jean Baptiste Perrin, ca. 1926
Born September 30 1870
Lille, France
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20th century - 21st century
1880s 1890s 1900s - 1910s - 1920s 1930s 1940s
1908 1909 1910 - 1911 - 1912 1913 1914
Year 1911 (MCMXI
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1880s 1890s 1900s - 1910s - 1920s 1930s 1940s
1908 1909 1910 - 1911 - 1912 1913 1914
Year 1911 (MCMXI
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Electron
Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Composition: Elementary particle
Family: Fermion
Group: Lepton
Generation: First
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Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Composition: Elementary particle
Family: Fermion
Group: Lepton
Generation: First
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